Selection towards different adaptive optima drove the early diversification of locomotor phenotypes in the radiation of Neotropical geophagine cichlids

Background: Simpson envisaged a conceptual model of adaptive radiation in which lineages diversify into \"adaptive zones\" within a broad adaptive landscape. However only a handful of studies have actually investigated the adaptive landscape and its implication for our interpretation of the underlying mechanisms of phenotypic evolution. In fishes the evolution of locomotor phenotypes may represent an important dimension of ecomorphological diversification during an adaptive radiation given its implications for feeding and habitat use. Neotropical geophagine cichlids represent a newly identified adaptive radiation and provide a useful system for studying patterns of locomotor diversification and the implications of selective constraints on phenotypic divergence in general. Results: We use multivariate ordination models of phenotypic evolution and posterior predictive approaches to investigate the adaptive landscape and test for evidence of early diversification of locomotor phenotypes in G...